This invention relates to construction elements of the kind comprising two plates of nailable material and web strips that hold the plates together in spaced apart relationship and consist of elongated sinuous sheet metal strips having teeth along their longitudinal edges embedded in the respective plates, and to a method and apparatus for the manufacture of such elements on a commercial scale.
More particularly, the invention relates to the manufacture of construction elements of the kind described in Ser. Nos. 327,924, now U.S. Pat. No. 3,872,641, and 497,828, wherein the preferred embodiment has the form of a closed box with bottom and top (flange plates) of a nailable plate material such as plywood, particle board or fibre board. The side walls (webs) of the element comprises sheet metal strips, such as galvanized steel, which are bent or corrugated in the transverse direction and shaped with dowel-like teeth along their longitudinal edges. The element is assembled in a pressing operation whereby the teeth of the web strips are pressed into the plates so as to provide a connection of considerable strength and stiffness.
In previous publications relating to structures of the above kind, such as German published Pat. No. 1,004,790 and U.S. Pat. No. 3,538,668, nothing is disclosed about how such elements may be produced, and especially how the web strips prior to the pressing operation can be held in their proper positions with a predetermined distance between the edges of the plates and the web strips, how completely closed elements should be manufactured, or how long elements may be pressed with a short press. As pointed out in applicant's above mentioned patent application, the shapes of web strips and teeth disclosed in the abovementioned previous publications, are not suitable for use in load-bearing elements and, as far as is known, have never found any practical use.
Load-bearing elements of the kind mentioned in the preamble may, in particular, be used as floor and roof elements in smaller buildings, such as residential houses, and will therefore have a place in modern commercial housing manufacture. It is feasible to manufacture such elements in modular dimensions, for example, in widths of 60 and 120 cm, if desired up to 240 cm, and in lengths up to 12 m.
For the bottom and top of a box-shaped panel element, particle board is a suitable material, because it is cheap and is produced in large sizes and at the present time also in qualities suitable for use in load-bearing components.
Very high dimensional precision is required if such elements are to be installed on the building site without appreciable finishing work such as sanding or puttying and form a sub-floor upon which floor covering such as linoleum or carpets are to be laid.
In order to ensure such dimensional precision and hence a correct fit between individual panels, the manufacturing method will have to meet a number of conditions which will be discussed briefly below.
Firstly, the web strips must be placed and kept in correct positions prior to the pressing operation. This means that they must be placed vertically between the bottom and top plates and stand straight along the plate edges, in the sense that the extreme points of the corrugated contour lie on a straight line which is parallel to the plate edges at a certain specified distance from these. Deviations in this respect complicate the sealing and connection between adjacent elements and give the finished elements an unsatisfactory appearance.
Secondly, the top and bottom plates should be held in correct relative positions so that the plate edges are at all points aligned in the vertical direction. If one plate is displaced relative to the other, problems will arise when the elements are to be installed and joined, since there will appear unsightly clearances between adjacent top or bottom plates. Actually, the mutual displacements between top and bottom plates should at no point exceed 1 mm, a requirement which for elements of a length of, say 8 m or more, call for rather rigorous measures.
Thirdly, the total height (thickness) of the panel after pressing should be kept within very close tolerances, for example .+-. 0.2 mm. Larger deviations in this dimension yield a noticable step in the joint between adjacent elements and call for additional finishing operations on the building site.
Fourthly, it is of considerable practical importance that the production machinery can quickly and simply be adjusted from one element size to another. This consideration applies to the length as well as to the width of the element and, to a smaller extent, also to the height.
Further, for the manufacture of large elements, it is important that the pressing of the element does not call for a press which is as long as the element itself, since a press of for example 12 m length would be very demanding with regard to both cost and space and, besides, could not be utilized to its full capacity.